Examples of a hand-held type or a portable type engine power tool using an engine as a drive source include a chain saw and a power cutter. In the chain saw, a saw chain, which is a chain-shaped saw blade for cutting a working object such as timber is provided in a power-tool main body. In the power cutter, a disk cutter for groove-forming or cutting of stone materials or concrete is provided in a power-tool main body. An engine mounted on such an engine power tool has an engine main body including a crankcase, to which a crankshaft is rotatably attached, and a cylinder, in which a piston is linearly reciprocatably built, and a cooling fan is attached to a first projecting end of the crankshaft so that the engine serves as a forcedly air-cooled engine. Cooling winds generated by the cooling fan are blown along the engine toward the opposite side of the engine with respect to the cooling fan to forcibly cool the engine. Since rotation of the cooling fan is stopped when the engine is stopped, the engine is cooled by natural air cooling after the engine is stopped.
To supply air-fuel mixture (vapor) of fuel and air to the engine, a vaporizer is attached to the engine via an insulator. When the engine is stopped, the flow of the air-fuel mixture in the vaporizer and the insulator is also stopped. As a result, the cooling effects of the vaporizer and the insulator brought about by the air-fuel mixture disappear. Therefore, heat conduction from the cylinder occurs in the vaporizer via the insulator and the temperature of the vaporizer increases. When temperature increase of the vaporizer becomes too large, most of gasoline, i.e., fuel evaporates. Therefore, sufficient fuel cannot be supplied from the vaporizer to the engine, and it becomes difficult to re-start the engine. Particularly, the engine used in the portable type engine power tool is strongly required to be downsized and is required to shorten the insulator as much as possible. Therefore, in the portable type engine power tool, in addition to the need to efficiently carry out forcible air cooling during engine operation, it has been an important technical problem to suppress temperature increase of the vaporizer without increasing the length of the insulator.
Japanese Patent Application Laid-Open No. 2001-123888 describes an engine which is configured to facilitate natural air cooling of a vaporizer by attaching a heat-dissipating fin between the vaporizer and an insulator.